JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014 - 45

toughening

New approaches to modifying the
impact toughness of RTM components
Integrating thermoplastic laid scrims between
the individual layers of carbon fibre fabrics can -
with a suitable combination of materials - lead to
a clear increase in impact resistance. Along with
the improved impact toughness, the discrete laid
scrims have further advantages when used with
resin infusion processes.

By
Prof. Dr. Markus Henne, University of Applied
Sciences Rapperswil
MSc Marcus Arnold, University of Applied
Sciences Rapperswil
Dr. Klaus Bender, Manager R+D Technical Fibers,
EMS-Chemie AG

ted with a resin-hardener mixture which is then cured under
high pressure and temperature (see Figure 1).

ibre-reinforced lightweight structures are currently enjoying increasing popularity in many technical applications.
For components manufactured in small and medium production runs of 1,000 to 20,000 parts per year, the resin transfer
moulding (RTM) process is being increasingly used because
of the high quality of the product and the cost efficiency of the
process. Current examples are aircraft parts and the safety cells
of the BMW i3 and i8 models as well as a variety of sports and
leisure articles.
RTM is a production process for the manufacture of highquality components in fibre-reinforced plastics that are capable
of withstanding high stresses. It is a resin injection process in
which the dry fibre structure is placed in a closed die and wet-

Fig. 1: Resin transfer moulding process

Epoxy resins are the most commonly used in the RTM process.
They are particularly easy to use, show low shrinkage on crosslinking, and possess outstandingly good mechanical properties,
such as for example their low tendency to creep. However, they
exhibit a brittle fracture behaviour under impact loading.
Given the growing use of the RTM process in the manufacture
of fibre-reinforced structures, it is important to investigate the
impact resistance of parts produced by this method and to take
any necessary steps to modify the process so as to improve the
impact toughness of such components.

Damage mechanisms in fibre-reinforced structures
A clear distinction must be made between low-speed impacts
such as those caused by a crash, bird strike
or turbine blade shedding and high-speed
impacts from shells and other projectiles,
or from bomb fragments. The two types
of impact lead to very different types of
damage. This article is concerned with
improving performance under low-speed
impact.
There are three types of damage: fibre
breaking, matrix cracking (intralaminar
rupture between the fibres), and delamination between the layers of fibres.
In practice, delamination is the most
problematic because the damage is not
readily discernible and its full extent can
only be assessed by costly non-destructive
testing (NDT) methods such as ultrasonic
No90 June - July 2014 /

jec composites magazine 45

JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #90 - June/July 2014